Keying out green screen causes grain on subject

So in my garage this is a homemade green screen we are using.  I understand that the lighting is off, but my subject is standing a few feet from the wall and have their own source of light.

Whenever I use Keylight to remove the screen and play the footage my subject gets this horrible grain to them.  This grain is not present when I play the green screen layer pre effect. 

Has anyone experienced this before and other than keylight, does Keylight cleaner help with this?  That kind of settings can I use for a clean removal.